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<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
let hhhh=55
        class Yin {
            constructor(a, b) {
                this.name = a
                this.age = b
            }
            test() { }
        }
        class fu extends Yin {
            constructor(a, b, c) {
                super(a, b)
                this.grade = c
            }

        }
        let yin = new fu('书莹', 18, '测试')
        console.log(yin)
    </script>
</body>

</html>